Asphalt mixes are commonly used as paving materials for road construction and maintenance. Typically, asphalt, often referred to as “asphalt binder” or “asphalt cement,” is mixed with aggregate to form material used in asphalt paving. Processing and use of this material by paving crews yields asphalt pavement. The asphalt pavement comprises aggregate held within a continuous phase of the asphalt binder by adherence of the asphalt binder to the aggregate.
The strength and durability of the asphalt pavement depends on various factors such as the properties of the materials used, the interaction of the various materials, the mix design, construction practices and the environment and traffic conditions that the pavement is exposed to. To produce a mix that will have good performance during the lifetime of the pavement, it is important to attain proper coating of the aggregate with the asphalt with the optimum asphalt binder film thickness, good adhesion of the asphalt onto the aggregate, and good cohesive strength of the asphalt.
Conventional pavements suffer from various types of distress modes such as permanent deformation, cohesive strength, oxidation and moisture damage. Permanent deformation is a significant problem for asphalt pavement. A road may be about 80 to about 100° F. or more warmer in the summer than it is in the winter. At warmer temperatures, asphalt pavement softens and can creep and move creating ridges and ruts, often referred to as “rutting,” under the weight of heavy trucks passing over it or traffic that has temporarily stopped, such as, for example, at a traffic light intersection, since rutting is dependent on both the weight of the vehicle and the time duration of the weight application. To reduce or prevent rutting, polymers or other materials having a relatively higher modulus than the asphalt, or that can produce a higher modulus asphalt binder at warmer temperatures than the asphalt, are often incorporated into conventional asphalt binders. Typical polymers used to modify asphalt binders to reduce or prevent rutting include elastomers, such as, for example, styrene/butadiene/styrene copolymer (SBS), and plastomers, such as, for example, polyethylene, ethyl/vinyl acetate copolymer (EVA), and the like.
Moisture damage is also a significant problem for conventional asphalt pavement. Because water has a higher affinity for the aggregate surface than does the asphalt binder and because there is effectively no or little chemical bonding between the asphalt binder and the aggregate surface, water can at times displace the asphalt binder from the aggregate surface causing moisture damage. This is known as “stripping.” To reduce or prevent stripping, anti-stripping additives are often incorporated into conventional asphalt binders. Common anti-stripping additives include amines that typically contain long, non-polar fatty chains that exhibit a high affinity for the asphalt binder. The molecular structures of these amines tend to increase the strength of the adhesive bond between the binder and the aggregate.
Unfortunately, the additives used to reduce or prevent stripping typically do not reduce or prevent rutting; similarly, the polymers used to reduce or prevent rutting typically do not reduce or prevent stripping. This can lead to more complex and costly asphalt pavement compositions that include both anti-stripping additives and anti-rutting polymers for resistance to stripping and rutting.
Accordingly, it is desirable to provide asphalt paving materials that include a polymer additive that is effective for reducing or preventing both stripping and rutting. In addition, it is desirable to provide methods for making such asphalt paving materials.